Sibling similarities and differences in their peer relations will be examined in a sample of siblings at risk for antisocial behavior and juvenile delinquency when each sibling is in middle school. Although the roots of variation in peer relationships are not well understood at the present time, there is increasing evidence that the family plays an important role in its development. Family experiences are conceptualized in terms of protective factors that promote children's peer relations or risk factors that hinder children's peer relations. Using a longitudinal sibling design, this study will explore the role of family processes in peer relations, and how these processes may be mediated via the emotion regulatory skills of the child. In particular, it will examine the parent-child system and the sibling system that may be associated with success and difficulty in peer relations. There will be 250 families consisting of a biological mother, a child in the 7th grade, and a same-sex full sibling in the 5th grade two years younger, all living in the same household, participating in this study. The sample can be broken down into two groups: (1) families with same-sex female siblings (N=125) and (2) families with same-sex male siblings (N=125). The primary hypothesis is that for these siblings in at-risk families, sibling similarities and shared family influences will be found in their dyadic interactions with their good friends and their peer group affiliation. Determining whether siblings growing up in the same family are at risk or protected differentially from poor peer outcomes will greatly contribute to our understanding of the individuals in peer relations.